Unusual Properties Of Staphylococcus Aureus Strains of the New Epidemic Phage Type-95

Abstract

SUMMARY. Three hundred and seventy-one penicillin-resistant Staphylococcus aureus strains of phage type 95 isolated in the years [1977][1978][1979][1980][1981][1982][1983] were investigated. They had characteristic resistance patterns to cadmium (Cd), arsenate (As) and mercury (Hg). Most were susceptible to all three heavy metals; 25 strains were resistant to As only and one to Cd and As. The susceptible strains had a uniform medium level of penicillinase production, whereas the As-resistant strains produced large amounts of penicillinase. In most of the strains, penicillin resistance was located on a very unstable penicillinase plasmid. The combinaton of rare properties found in Danish type-95 strains seems to point to the spread of one or two clones. Co-reactions with other phage groups or complexes and results of lysogenisation experiments suggest that the Danish type-95 strains are derived from strains of the 52, 52A, 80, 81 complex. INTRODUCTIONWhen staphylococci of the 52, 52A, 80, 81 and 83A phage-type complexes appeared, it was possible to designate probable ancestor(s) by demonstrating evolutionary processes that might have operated (Asheshov and Winkler, 1966;Jevons et al., 1966). The results of these investigations led to the assumption that strains of phage type 80/81 might belong to one clone (Asheshov and Winkler, 1966), whereas members of the 83A complexes might have different ancestors .In recent years, strains of phage type 95 have spread in Denmark. Among Staphylococcus aureus isolates from cases of bacteraemia, the occurrence increased from I % in 1972 to 9% in I98 I (Rosendal et al., I983), and among the 20 000 strains phage-typed in Denmark in 1983,12% were of phage type 95. The present investigation considers the one-clone theory in relation to type-95 strains spreading in Denmark. A total of 3 108 strains isolated from cases of bacteraemia from 1977-1 982 were surveyed for loss of penicillin resistance in the period between primary isolation and the second testing for antibiotic susceptibility (table I, part 1). From this material, 46 strains were chosen for further investigation of the stability of the penicillinase property (table I, part 2). MATERIALS AND METHODS StaphylococcusFive penicillin-resistant strains, all isolated before 1977, with heavy-metal resistance to arsenate only, were examined quantitatively for penicillinase production. Two of them belonged to the 83A complex and one each to groups I, I1 and 111.The relationship between strains of phage type 95 and other strains was studied in 2586 strains isolated from cases of bacteraemia during 1977-1 98 I . The 2586 strains included penicillin-resistant and penicillin-susceptible strains, but strains lysed by phage 95 only (at routine test dilution; RTD) were omitted. The 2586 strains were surveyed for sensitivity to typing phage 95; a similar survey was made of all 31 1 strains of the 52, 52A, 80, 81 complex isolated from [1970][1971][1972][1973][1974][1975][1976].Phage typing was performed according to the methods of Blair and ...

QUANTITATIVE DETERMINATION OF β‐LACTAMASE PRODUCTION IN STAPHYLOCOCCUS AUREUS STRAINS COMPARED TO QUALITATIVE TESTING BY A MICROBIOLOGICAL CLOVER LEAF TEST, A CHROMOGENIC CEPHALOSPORIN TEST AND A IODOMETRIC TEST

“…The difficulties in using the chromogenic cephalosporintest suggests that the p-lactamase produced by strains of phage type 95 may have low affinity for cephalosporins. Furthermore, the strains of type 95 have in a previous study (16) been found to lose its P-lactamase plasmid very easily by storage of the strain. False negative results when testing for p-lactamase production is therefore a risk if the strain is not totally freshly cultured.…”

“…This problem has already been observed in our laboratory. The problems with strains of the phage type 95 are of some concern since these strains are increasing in number these years ( 16).…”

Staphylococcus aureus strains of type 95. Spread of a single clone

“…Previous investigations on S. aureus strains of type 95 including only betalactamase production and heavy metal resistance pointed to the possibility that all the As-resistant strains belonged to one single clone, and that the remaining few strains with As-resistance and high beta-lactamase production might either be a totally separate, not so widespread, clone or might be a variant of the original clone with a change in the beta-lactamase plasmid including introduction of Asresistance [7]. In the present investigations three newer typing methods: multilocus enzyme electrophoresis, pulsed-field gel electrophoresis and lectintyping have been selected to represent three fundamentally different typing principles: phenotypically expressed differences in the produced isoenzymes and surface-components as well as differences in the gene-sequences.…”

“…During [7], and comprised 10 strains with high beta-lactamase production and As-resistance (strain nos 1, 5, 7, 9, 10 and 31-35) and 10 susceptible strains with medium production. In addition, 15 [1].…”

“…With the old multiply resistant strains of the 83A complex, different prophages were introduced on different occasions into Group III strains causing a shift to the 83A complex and the high usage of antibiotics, especially tetracycline, was an effective selection pressure combined with frequent crossinfection. With the recent strains of type 95, however, only penicillin usage might act as the selective pressure and would select not only strains of type 95 but also strains of many different phage types; in addition improved hospital hygiene had reduced cross-infection and preliminary investigations seemed to indicate that strains of type 95 belong to only one or two bacterial clones [6,7], which spread slowly.…”